1. Field of the invention
The present invention relates to a liquid sealed type cylindrical anti-vibration apparatus used for such as an engine mount of an automotive vehicle.
2. Description of the Prior Art
Such a liquid sealed type cylindrical anti-vibration apparatus is well known which comprises an outer cylinder and an inner cylinder which are arranged with each other at an inside and an outside. In the device, an elastic member tightly connects these outer and inner cylinders by means of baking or the like and is formed of rubber as an anti-vibration body. A main liquid chamber and an auxiliary liquid chamber are provided between a liquid chamber recess formed on a part of the elastic member and the outer cylinder, these chambers are filled with working liquid and communicate with each other with an orifice passage. Some apparatus have a partition wall, which is formed at a part of the elastic member and separates the main liquid chamber and the auxiliary liquid chamber, which is formed to have relatively a thin thickness and set to a membrane-resonate by liquid flow in the liquid chambers. Other apparatus is provided with a member (hereinafter described as a medium to high frequency device) spread as an umbrella shape from the inner cylinder into the main liquid chamber so as to generate resonance by the elastic member in a medium to high frequency range.
A curve shown as a comparative example 1 in characteristics curve shown in FIG. 15 is that of an apparatus having a construction in which an elastic member is connected with an outer cylinder and the medium to high frequency device is provided therewith. With the construction, a dynamic spring constant can be reduced in a frequency range having about 200 Hz band width from about 300 to 500 Hz width in a medium frequency range by virtue of the medium to high frequency device.
Recently, it is required to lower the dynamic spring constant in wider frequency band in the medium to high frequency range. To achieve this purpose, it is considered that a partition wall is formed to be a thin thickness as stated previously so as to generate membrane resonance and the elastic member is arranged not to be connected with the outer cylinder. A characteristic curve of an apparatus in which this idea is adopted is shown as a comparative example 2, which actualize a further lower dynamic spring constant in a higher frequency range than 500 Hz. In both examples however, it is difficult to realize a low dynamic spring constant over wider band in high frequency range. A principal purpose of the present invention is to meet such a request to realize the low dynamic spring constant over wider band in the high frequency range and to expand the range to the medium to high frequency.
In order to solve the above subject, according to the present application there is provided a liquid sealed type cylindrical anti-vibration apparatus comprising: an outer cylinder and an inner cylinder arranged to be radially apart from each other; an elastic member connecting the outer cylinder and the inner cylinder; a main liquid chamber and an auxiliary liquid chamber interposed between a liquid chamber recess formed on a part of the elastic member and the outer cylinder; the main liquid chamber and the auxiliary liquid chamber are filled with working liquid, and communicated each other with an orifice passage; wherein a partition wall, which divides the main liquid chamber and the auxiliary liquid chamber, is formed by means of a part of the elastic member and is set to resonate by membrane in a medium to high frequency range. Further, the apparatus comprises a pair of end walls formed on a part of the elastic member extending in a radial direction at axially both end regions of the inner cylinder as a part of the wall portion surrounding the liquid chamber recess, these end walls are set to resonate by membrane in a medium to high frequency range, and the partition wall and the end wall are set to resonate cooperatively in a medium to high frequency range.
Since a partition wall and an end wall are set to respectively resonate by membrane in the medium to high frequency range, each wall contributes to lower a dynamic spring constant in the medium to high frequency range. Moreover, since the partition wall and the end wall resonate cooperatively, a frequency range where the dynamic spring constant is made lower is more broaden. As a result, the dynamic spring constant is made lower over much wider range than the former one.
In the present application, an axial direction is directed to a direction parallel to an axis line of the inner or outer cylinders, by a circumferential direction, a similar direction of the circumferential direction of the inner or outer cylinder, and by a radial direction a direction parallel to a radial direction of the inner or outer cylinder.
An outer peripheral portion of the partition wall may be unconnected and intimately contacted to an inside of the outer cylinder. Thereby the dynamic spring constant can be made lower in the frequency band having already lowered dynamic spring constant in the medium to high frequency range.
The liquid chamber recess of the elastic member may be covered by an auxiliary liquid chamber cover and a main liquid chamber cover. A stopper is provided to project into the main liquid chamber integrally with the main liquid chamber cover. A top portion of the stopper is arranged to be broad and a passage portion is formed around the stopper to resonate by liquid column in a medium frequency range by liquid flow accompanied by the volume variation in the main liquid chamber.
A stopper integrated with the main liquid chamber cover is used also as a medium to high frequency device which resonate by liquid column in the medium to high frequency range by means of liquid flow accompanied with volume variation in the main liquid chamber. This can realize a low dynamic spring constant in the medium to high frequency range and it become easy to form such a medium to high frequency device.
The orifice passage may be formed on an outer cylinder side surface of the liquid chamber cover covering the liquid chamber recess of the elastic member an may be connected with a similarly formed orifice passage of the elastic member. When the connected portion is viewed as a cross-section in a radial direction, an abutting face on the end region of the elastic member is slanted so that as it gets nearer to an inside, so that it overlaps more to the abutting face of the end region of the liquid chamber cover. Thereby sealing on a connecting portion between the elastic member and the liquid chamber cover can be secured. Since liquid leak can be prevented even if the orifice passage is continuously connected at the connecting portion, a long orifice passage can be easily formed.
The elastic member which partially forms the end wall is interposed between the outer peripheral ring and the inside of the outer cylinder. This portion functions as a rubber spring portion of a mass damper to control vibration input and serves to lower the dynamic spring constant.
On an outer surface of the elastic member and at a medium portion in a width direction, a seal lip having a substantially inverted-U shape in a cross-section may be formed integrally with the elastic member and on the entire periphery thereof. This makes the elastic member hard to be broken when it is press-fitted into the outer cylinder. Therefore, since the device can be assembled by press fitting, not by squeezing as in a conventional method, workability is improved.
In an axial cross-section of the elastic member the outer periphery thereof may be projected outwardly more than the seal lip which is formed on an outer peripheral end face of the end wall. This possibly makes a static spring constant of the partition wall to change by press fitting and cooperative resonance can be easily controlled.
An outer periphery of the inner cylinder may be formed in a shape having a non-circular cross-section, a thick wall cover using a different material is provided on a periphery thereof and a part facing to the main liquid chamber is formed in a flat shape.
A substantially umbrella-shaped medium to high frequency device may be provided, which projects into the main liquid chamber from the inner cylinder and set to resonate by liquid column in a high frequency range. This makes it possible that the dynamic spring constant is lowered in further higher frequency range. This result in that the dynamic spring constant can be lowered over wider frequency range spreading to high frequency range.
A drop off stopper may be provided by bending an end of the outer cylinder in a center direction and claw shaped projections may be discontinuously provided on another end. An inserted body which is integrally composed of the inner cylinder, the elastic member and the liquid chamber cover is inserted from the claw shaped projections side, and the outer cylinder and the inserted boy are integrated by bending the claw shaped projections. This enables to assemble the device by simple caulking work.